There are four blue marbles, an unknown number of red (r) marbles, and six yellow marbles in a bag. Which expression
represents the probability of randomly selecting a blue marble, replacing it, and then randomly selecting a red marble?
A. 4/10 (r/10)
B. 4/10r ( r/10r)
C. 4/10+r (r/10+r)
D. 4/10 + (r/10r)